Kerr effect

The Kerr effect (more specifically: the electro-optical Kerr effect) is an effect of non-linear optics. It (such as the Pockels effect ) is a special case of a general electro-optic effect, and describes the change in the optical properties of a material by applying an external electric field. It is applied for example in the Kerr cell and the Kerr - lens.

History

The Kerr effect is named after the Scottish theologian and physicist John Kerr (1824-1907) named, who discovered it in 1875. The above-described Kerr effect is also referred to as a square electro-optical effect, in contrast to the 1876 found magneto-optical Kerr effect.

Explanation

Applying an electric field to a medium changes its optical properties, among other things, because it causes a (non-linear ) realignment or reorientation of the various carriers in the material. This process draws inter alia, a change in the refractive index of the material according to you, which can be mathematically developed by a Taylor series:

The higher orders of the nonlinear refractive index can be determined using the Kramers-Kronig relation of the frequency-dependent absorption of the medium. The term causes the electric Kerr effect, whereas, the optical Kerr effect describes the case in which all the parameters relative to the parameter can be neglected: the material exhibits a change in the refractive index of ordinary (o) and extraordinary ( e) axis is proportional to the square of the applied electric field strength:

The result is that the material can produce a birefringence. The "strength " of the Kerr effect depends on the material properties. He is in some transparent media such as some crystals and liquids particularly strong and thus can be easily observed. Further, the Kerr effect is dependent on the direction of propagation and polarization of the light in the material and the direction and strength of the electric field relative to the crystal axes.

In most cases caused by the Kerr effect of the change in refractive index is minimal: in crystals of the order of 10-4 and 10-9 in liquids. If, however, in the light material over a longer distance (read: a few thousand wavelengths) travels, the effect is cumulative and can be obtained by applying the electric field, a phase shift of 0 to achieve.

Other approach

The Kerr effect describes the influences on the polarization state of light due to external electric fields. The starting point is an optically isotropic medium (eg, fluids), in which there are anisotropically polarizable, ie elongated molecules. By applying an external electric field a dipole moment is induced resulting in an orientation of the majority of these molecules are elongated. Although, due to the thermal activity of the fluids ( e.g., water) molecules are not aligned, the sufficient number of the aligned molecules to cause double refraction.

This is replaced by the parallel polarized light to a different refractive index, namely

With as an extraordinary refractive index

And

With as an ordinary refractive index.

The difference between the two is:

With

• The wavelength
• A constant K.